In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
Modern engine blocks for passenger cars are often made of aluminum with cast iron liners. For the machining of these coated cemented carbides and Polycrystalline Diamond (PCD) inserts are generally used. Coated carbides can not be used at cutting speeds above 600 m/min and higher due to too high thermal load. PCD inserts function well but are not competitive due to high cost. Wet milling is used due to surface finish and chip evacuation. Emulsions used in machining are environmental and health problems and lead to a higher cost. Cutting data are; Cutting speed approximately 150-300 m/min and feed-rate/tooth around 0.15-0.30 mm/tooth. Depth of cut is between 0.2 and 1.5 mm.
In general engine blocks are produced in transfer lines and the time pressure is high. Often this operation is a bottleneck in the production. Milling cutters with close pitch are used which leads to change of about 30-40 inserts when they are worn out. One typical wear mechanism is built up edge which leads to a bad surface finish and failure of the cutting edge which leads to rapid wear. The main reason for tool change is surface finish and demands are high which leads to frequent tool changes.
Silicon nitride is a cutting tool material for machining of cast iron due to its good wear resistance and good high temperature properties. The properties of silicon nitride are greatly dependent on the density, and it has been found necessary to add sintering aids to silicon nitride in order to fully densify the body. Typically the sintering aids used are Al2O3, BeO, MgO, TiO2, ZrO2, HfO2 and the oxides of the Group III elements of the periodic table scandium, yttrium, lanthanum, cerium, etc. The amount of sintering aid added is of the order of a few wt-%. The sintering aids form during sintering a glass phase, which facilitates the densification. Silicon nitride cutting inserts thus consist of beta silicon nitride in an intergranular glass phase.
It is an extremely high demand to develop tool solutions with a long tool life and less frequent tool changes. Dry machining of these type of applications is a strong demand in order to reduce costs, health hazards and environmental impacts.